(a) Field of the Invention
The present invention relates to a quasi-orthogonal space-time block coding system and method.
(b) Description of the Related Art
In a mobile communication system, a channel state is changed in various ways with respect to time because of fading and interference generated in the channel. In this condition, when the same signal is transmitted by a plurality of antennas of a transmitter, a receiver acquires a diversity gain by combining signals that are receiving from different channel environments, thereby improving system performance.
The space-time block coding (STBC) skill is to simultaneously encode the same information into different formats at a plurality of antennas, transmit them to the receiver, and thereby acquire the diversity gain. One of the most popular ways of the skill is to send two different encoding signals for the same information through two transmit antennas. In this skill, two symbols during two symbol period are encoded two different forms, and they are transmitted through two antennas. The encoding method used in this skill provides full orthogonality, and this allows a simple linear decoding at the receiver and the maximum diversity gains. An encoding rate of this skill is 1 because the number of symbols that are transmitted at respective antennas is one during a single symbol interval.
In general, in the transmission diversity method using a plurality of antennas, the diversity gain is increased as the number of antennas is increased. However, when the number of transmitting antennas is at least 3, the orthogonal STBC (O-STBC) method having the encoding rate of 1 cannot exist, and hence, it is required to use the method having an encoding rate that is less than 1 in order to acquire the sufficient diversity gain.
Therefore, the encoding rate of the O-STBC method using three or four transmitting antennas is given as 0.5 or 0.75. Reduction of the encoding rate results in a reduction in a signal data rate, hence reducing spectral efficiency.
In order to overcome the drawback, various quasi-orthogonal space-time block coding (QO-STBC) techniques having the encoding rate of 1 have been proposed. However, since the quasi-orthogonal space-time block coding methods do not maintain complete orthogonality, a decoding algorithm of the receiver becomes very complicated. Further, since the complete orthogonality is not maintained, interference of an adjacent signal exists when detecting a received signal, and the system performance is deteriorated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.